By Janet Raloff
On Oct. 26, 1948, a temperature inversion laid a blanket of cold, stagnant air over Donora, Pa., a tiny mill town on the Monongahela River. Over the next 5 days, the buildup of pollution cloaked the sun, sometimes restricting vision to just a few feet. Twenty people died outright and 50 more perished within a month from lingering health damage, says consulting epidemiologist Devra Davis, a former Donora resident whose own family survived the tragedy.
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As bad as her hometown’s pollution had been, its impact would pale against a 5-day killer smog that settled on London in December 1952. It killed some 12,000 people within 3 months, according to calculations in a June 2001 report by Davis and Michelle L. Bell of Johns Hopkins University in Baltimore. “With a death rate more than three times the norm for this period, the London fog of 1952 is widely regarded as a catalyst for the study of air pollution epidemiology,” the pair noted.